fix: correct Dense input dim in BroNet and respect multiplier in SimbaBlock

[Copilot]

Two bugs in the newly added BroNet and Simba modules that would cause runtime errors or silently ignore a user-configurable parameter.

Fixes

• bronet.py: nn.Dense(self.hidden_dims, ...) passed a Sequence[int] where an int is required. Fixed to nn.Dense(self.hidden_dims[0], ...) — safe because setup() already asserts all dims are equal.

• simba.py: SimbaBlock hardcoded the expansion factor as hidden_dim * 4, making the multiplier field on both SimbaBlock and Simba a no-op. Fixed to hidden_dim * self.multiplier.

# Before — multiplier param had no effect
x = nn.Dense(self.hidden_dim * 4, kernel_init=init.he_normal())(x)

# After — honours the configurable multiplier
x = nn.Dense(self.hidden_dim * self.multiplier, kernel_init=init.he_normal())(x)

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